Reducing asymmetrically deposited film induced registration error

ABSTRACT

Methods, systems, products and apparatuses are disclosed herein relating to registration and asymmetrically deposited films, and more specifically, to reducing asymmetrically deposited film induced registration measurement error.

FIELD OF THE INVENTION

[0001] The present invention generally relates to semiconductorprocessing for integrated circuits. In one aspect, the present inventionrelates to reducing error in layer-to-layer overlay alignment. Inanother aspect, the invention relates to registration methods forasymmetrically deposited films, and more specifically, methods forreducing asymmetrically deposited film induced registration measurementerror.

BACKGROUND OF THE INVENTION

[0002] Integrated circuits (IC's) are formed by sequentially creatinglayers on an integrated circuit substrate, such as a semiconductorsubstrate. These layers can include: insulating layers, polysiliconlayers, and conducting layers, such as silicide or metal layers. Thelayers can be patterned or etched to form IC parts or features (e.g.,electronic components, interconnections and the like).

[0003] For an IC to operate properly, structures within overlying layersmust properly align with one another. However, as integrated circuitsbecome more dense and complex, it is becoming increasingly difficult toachieve registration of overlying structures. Misalignment between thelayers can be a limiting factor in achieving increased IC integrationdensity and a functioning device.

[0004] Generally, registration of one patterned layer with another canbe achieved using special registration marks that are designed into eachlayer. When the registration marks of one patterned layer are registeredwith those of a previously patterned layer, it can be assumed that theremainder of the patterned layer is also properly registered with thatof the previously-patterned layer.

[0005] Monitoring and adjustment of the alignment process was originallyperformed by human operators using a microscope. The decreasing size ofintegrated circuit features and layers, and the increasing number oflayers per wafer, have contributed to the development of automatedalignment processes using specialized tools known in the art. Suchtools, including but not limited to: proximity printers, projectionprinters, aligners and steppers, generally provide systems, methods andcomputer program products for aligning a pattern with respect tounderlying or previous patterns, and/or to the underlying substrate.Such exposure tools (also called a “patterning tool”) are described ingreater detail, for example, in U.S. Pat. No. 6,064,486, the disclosureof which is incorporated by reference herein.

[0006] The registration mark(s) (also referred to herein as “overlaymark(s)” and “registration measurement structures”) may not besymmetrical, however, thus making it more difficult to find the centerposition of the registration mark. Moreover, even if the registrationmark is symmetrical, subsequent processing can create an asymmetriccoating that can include one or more additional layers on or adjacent tothe registration mark. Asymmetry in such a coating, or in the markitself, can result in an asymmetric registration signal that can causeregistration of a patterned structure to be measured or perceivedincorrectly.

[0007] If the registration structure comprises a raised feature orcomponent (e.g., a mesa) or a depressed feature or component (e.g. atrench) on an integrated circuit substrate, one or more material layersmay be formed onto the feature. Such layers can be formed asymmetricallyover the feature due to the topography of the feature (e.g., raised ordepressed), itself and/or due to asymmetries in the film or coatingforming process. For example, metal deposition and photoresist film orcoatings processes can produce asymmetries over the surface of asubstrate. Such asymmetric films can make it difficult to accuratelydefine the centerline of the registration mark, and thus, induce anasymmetric film registration error that can cause misalignment betweenconsecutive layers of an IC.

[0008] Deposition processes are referred to as “metal depositionprocesses” when the material layer being deposited is a metallicmaterial. Sputtering of a metal onto a silicon wafer is one specificexample of an “asymmetric deposition process”. Sputtering techniques(also known as physical vapor deposition or “PVD”) are well known in theart. See Wolf and Tauber, Silicon Processing for the VLSI Era, Vol. 1,Chpt. 11, (Lattice Press 2000); Zant, Microchip Fabrication, pp. 411-16(McGraw-Hill 2000); and Aronson, “Fundamentals of Sputtering”,Microelectronics Manufacturing and Testing, January 1987. Examples ofconventional sputtering techniques include high density plasma (HDP) orcollimated sputtering. Another exemplary conventional sputtering processis the sputtering of aluminum for metal interconnects.

[0009] Attempts have been made to reduce and/or eliminate registrationerror caused by asymmetrically deposited films. For example, onesolution has included an attempt to develop distinctive overlay marks,such as “chopped overlay marks”. However, while such overlay marks canwork to affect the way asymmetric films are deposited, currentregistration tools and associated methods for their use have heretoforebeen unable to appropriately obtain accurate registration data. This hasbeen the case for a variety of reasons, one of which is that the metalfilm that is deposited on registration marks can appear opaque to abroadband light of the kind typically used in current registrationtools.

[0010] Accordingly, it would be desirable to provide methods,apparatuses and systems for reducing asymmetric film inducedregistration error in the semiconductor industry.

SUMMARY OF THE INVENTION

[0011] The present invention relates generally to semiconductorfabrication techniques and, more particularly, to the reduction, andpotentially the elimination, of asymmetric film induced registrationerror is disclosed herein. The method, apparatuses, and systemsdisclosed herein ideally solve the aforementioned problems and reducesuch false overlay error in a cost-effective manner.

[0012] In one aspect, the invention provides methods for reducingregistration measurement error due to an asymmetrically deposited filmusing critical dimensions. The method employs a registration measurementstructure formed in overlying upper and lower layers of a semiconductorconstruction, the lower layer comprising a first component of theregistration measurement structure, and the upper layer comprising asecond component of the registration measurement structure, the firstcomponent comprising a first edge and a second edge, and a firstdistance from the first edge to the second edge, and the secondcomponent comprising a first edge and a second edge. An exemplaryregistration structure comprises a box-in-box registration structure.One hallmark of the method is that critical dimensions of an overlaystructure can be determined, and using the critical dimensiondeterminations in conjunction with overlay measurements, registrationerror can be substantially reduced, and potentially eliminated.

[0013] In one embodiment of the method, the method comprises acquiringdata from the first component of the registration measurement structureto provide a first critical distance value from the first edge to thesecond edge; acquiring data from the position of the first component inrelation to the second component to provide an apparent registrationmeasurement; acquiring data from the first component having anasymmetrical film layer deposited thereon, to provide a second criticaldistance value from the first edge of the first component to an edge ofthe film layer disposed contiguously to the first edge of the firstcomponent; comparing the second distance value to the first distancevalue to generate an alignment error value corresponding to a thirddistance value measured from said edge of the film layer to the secondedge of the first component; comparing the apparent registrationmeasurement and the third distance value to remove the alignment errorand generate an actual registration value; and conveying the actualregistration value to a patterning apparatus for aligning a subsequentlayer to the structure.

[0014] In another embodiment, the method comprises determining a firstcritical dimension of the registration structure; determining anapparent registration measurement of the registration structure;measuring a second critical dimension of the registration structure whenthe registration structure comprises an asymmetrically deposited film;using the first critical dimension and the second critical dimension todetermine the registration measurement error of the registrationstructure due to the asymmetrically-deposited film; subtracting theregistration measurement error from the apparent registrationmeasurement of the registration structure to generate a corrected datarepresentative of an actual registration of the registration structure;and conveying the actual registration data to a patterning apparatus toalign a subsequently patterned layer relative to the structure.

[0015] In another aspect, the invention provides methods for reducingregistration measurement error due to an asymmetrically deposited filmusing gate imaging techniques. The method likewise uses a registrationmeasurement structure as described hereinabove, which has a centerlinevalue.

[0016] In one embodiment of the method, the method comprises obtaining apair of gate images of the first material layer (first component) of theregistration structure; determining an image centerline value of each ofthe images of the first material layer; averaging the image centerlinevalues of the first material layer images to provide a first offsetcenterline value; obtaining a pair of images of the second materiallayer of the registration structure; determining an image centerlinevalue of each of the images of the second material layer; averaging theimage centerline values of the second material layer images to provide asecond offset centerline value; comparing the first offset centerlinevalue with a second offset centerline value to provide a first deltavalue (AI); manipulating the pair of images of the first material layerto obtain flipped images of the first material layer; determining animage centerline value of each of the flipped images of the firstmaterial layer; averaging the image centerline values of the firstmaterial layer flipped images to provide a third offset centerlinevalue; comparing the third offset centerline value to the second offsetcenterline value to provide a second delta value (Δ₂); subtracting theΔ₁ value from the Δ₂ value to provide a Δ_(s) value, and averaging theΔ_(s) value to provide a registration measurement error; subtracting theregistration measurement error from the registration structurecenterline value to generate a corrected data representative of anactual centerline value of the registration structure; and conveying theactual centerline value of the registration structure to a patterningapparatus to align a subsequently patterned layer relative to theregistration structure.

[0017] In another embodiment, the method comprises obtaining a pair ofimages of the first material layer of the registration structure;determining an image centerline value of each of the images of the firstmaterial layer; averaging the image centerline values of the firstmaterial layer images to provide a first offset centerline value;obtaining a pair of images of the second material layer of theregistration structure; determining an image centerline value of each ofthe images of the second material layer; averaging the image centerlinevalues of the second material layer images to provide a second offsetcenterline value; comparing the first offset centerline value with asecond offset centerline value to provide a first delta value (Δ₁);manipulating one of the pair of images of the first material layerresulting in a flipped image and a non-flipped image of the firstmaterial layer; determining an image centerline value of the flippedimage and the non-flipped image of the first material layer; averagingthe image centerline values of the flipped image and the non-flippedimage of the first material layer to provide a third offset centerlinevalue; comparing the third offset centerline value to the second offsetcenterline value to provide a second delta value (Δ₂); subtracting theΔ₁ value from the Δ₂ value to provide a Δ_(s) value corresponding to aregistration measurement error; subtracting the registration measurementerror from the registration structure centerline value to generate acorrected data representative of an actual centerline value of theregistration structure; and conveying the actual centerline value of theregistration structure to a patterning apparatus to align a subsequentlypatterned layer relative to the registration structure.

[0018] In another embodiment, the method comprises obtaining a pair ofimages of the first material layer of the registration structure;manipulating one of the pair of images of the first material layerresulting in a first flipped image and a non-flipped image of the firstmaterial layer; determining an image centerline value of the firstflipped image and the non-flipped image of the first material layer;averaging the image centerline values of the first flipped image and thenon-flipped image of the first material layer to provide a first offsetcenterline value; obtaining a pair of images of the second materiallayer of the registration structure; determining an image centerlinevalue of each of the images of the second material layer; averaging theimage centerline values of the second material layer images to provide asecond offset centerline value; comparing the first offset center linevalue with a second offset centerline value to provide a first deltavalue (Δ₁); manipulating a second of the pair of images of the firstmaterial layer resulting in first and second flipped images of the firstmaterial layer; determining an image centerline value of the secondflipped image of the first material layer; averaging the imagecenterline values of the first and second flipped images to provide athird offset centerline value; comparing the third offset center linevalue to the second offset centerline value to provide a second deltavalue (Δ₂); subtracting the Δ₁ value from the Δ₂ value to provide aΔ_(s) value corresponding to a registration measurement error;subtracting the registration measurement error from the registrationstructure centerline value to generate a corrected data representativeof an actual centerline value of the registration structure; andconveying the actual centerline value of the registration structure to apatterning apparatus to align a subsequently patterned layer relative tothe registration structure.

[0019] In another embodiment, the method comprises obtaining at leasttwo images representative of a registration site that comprises anasymmetric deposition layer; measuring the images to obtain a first dataset; flipping the two images to obtain flipped images; measuring theflipped images to obtain a flipped data set; comparing the first dataset to the flipped data set to obtain an amount corresponding to thedifference between the first and flipped data sets; removing thedifference so as to obtain a true site offset data set substantiallyfree of site error; and outputting the true site offset data set tocounter registration site non-uniformity.

[0020] In another aspect, the invention provides a system for reducingregistration measurement error caused by asymmetric film deposition. Inone embodiment, the system comprises means for determining a firstcritical dimension of an alignment structure when the alignmentstructure is free of a asymmetrically deposited film; means formeasuring a second critical dimension of the alignment structure whenthe structure includes an asymmetrically deposited film; means forcomparing the first critical dimension to the second critical dimensionto obtain an offset amount; and means for using the offset amount toachieve reduced registration measurement error due to the asymmetricallydeposited film, the error reduced between the one layer and anotherlayer in the integrated circuit.

[0021] In another aspect, the invention provides a system providingmeans for reducing registration measurement error cause by asymmetricfilm deposition using gate images.

[0022] In another aspect, the invention provides a computer readablemedium on a computer. The computer readable medium comprises computerexecutable instructions for the foregoing methods.

[0023] In yet another aspect, the invention provides a computerprogrammed product for reducing registration measurement error usingcritical dimensions. In one embodiment, the computer program productcomprises a computer readable storage medium having a computer-readableprogram code means embodied in the medium, and the computer-readableprogram code means comprises computer-readable program code fordetermining a first critical dimension of an alignment structure whenthe alignment structure is free of an asymmetrically deposited film;computer-readable program code for measuring a second critical dimensionof the alignment structure when the structure includes an asymmetricallydeposited film; computer-readable program code for comparing the firstcritical dimension to the second critical dimension to obtain an offsetamount; and computer-readable program code for using the offset amountto achieve reduced registration measurement error due to theasymmetrically deposited film.

[0024] In yet another aspect, the invention provides a computerprogrammed product for reducing registration measurement error usinggate images. The computer program product comprises a computer readablestorage medium having a computer-readable program code means embodied inthe medium, and the computer readable program code means comprisescomputer-readable program code for accomplishing the registrationmeasurement error reduction.

[0025] In yet another embodiment, the invention provides a registrationsystem. In one embodiment, the registration system comprises: (a) aregistration measurement structure disposed within overlying layers of asemiconductor construction, a first component of the registrationmeasurement structure disposed within a first layer of the semiconductorconstruction and comprising first and second edges and a distancetherebetween, and a second component of the registration measurementstructure disposed within a first layer of the semiconductorconstruction and comprising first and second edges; (b) a registrationapparatus operable for acquiring image data of: i) the first and secondedges of the first component, ii) the first and second edges of thesecond component, iii) an edge of a film layer asymmetrically depositedonto the second edge of the first component, and iv) the first or secondedge of the first component in relation to the first edge of the secondcomponent; (c) a processor operable for producing distance valuesbetween said edges from the acquired image data, the distance valuescomprising (i) a first distance measured from the first edge to thesecond edge of the first component, and ii) a second distance measuredfrom the first edge of the first component to the edge of theasymmetrically 5 deposited film layer; (d) the processor furtheroperable for producing an apparent registration measurement of the firstcomponent in relation to the second component based on measurements ofthe first or second edge of the first component to the first edge of thesecond component; (e) the processor further operable for comparing thesecond distance value to the first distance value to generate analignment error value corresponding to a third distance between the edgeof the asymmetrically deposited film layer and the second edge of thefirst component; (f) the processor further operable for comparing theapparent registration measurement and the alignment error value togenerate an actual registration value corresponding to the position ofthe second component relative to the first component; and (g) theprocessor further operable to convey the actual registration value to apatterning apparatus for aligning a subsequent layer to the registrationmeasurement structure.

[0026] In yet another embodiment, a registration system is providedsimilar to that described in the previous paragraph in whichregistration system accomplishes registration measurement errorreduction using gate images.

[0027] Various other embodiments, features, objects and advantages ofthe present invention will be made apparent from the following detaileddescription and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The various features, objects and advantages of this inventionare best understood with reference to the preferred embodiments whenread in conjunction with the following drawings.

[0029]FIG. 1A shows an enlarged schematic top view of a conventionalbox-in-box registration structure.

[0030]FIG. 1B shows an enlarged schematic cross-sectional view takenalong line 1B-1B of FIG. 1A.

[0031]FIG. 2A shows an enlarged schematic top view of a box-in-boxregistration structure comprising an asymmetrically deposited materiallayer.

[0032]FIG. 2B shows an enlarged schematic cross-sectional view takenalong line 2B-2B of FIG. 2A.

[0033]FIG. 2C shows another embodiment of a registration measurementstructure comprising a recessed component and an asymmetricallydeposited film layer

[0034]FIG. 3A shows an enlarged schematic top view of a box-in-boxregistration structure comprising an asymmetrically deposited materiallayer.

[0035]FIG. 3B shows an enlarged schematic cross-sectional view takenalong line 2B-2B of FIG. 2A.

[0036]FIG. 3C shows a pair of enlarged measurement gate images of theouter box of the box-in-box registration structure of FIGS. 3A-3Bcomprising an asymmetric deposition layer.

[0037]FIG. 3D shows a pair of enlarged measurement gate images of theouter box of the box-in-box registration structure of FIGS. 3A-3Bcomprising an asymmetric deposition layer, the pair of images rotatedwith respect to the images of FIG. 3C.

[0038]FIG. 3E shows a pair of enlarged measurement gate images of theouter box of the box-in-box registration structure of FIGS. 3A-3Bcomprising an asymmetric deposition layer, one of the images rotatedwith respect to the images of FIG. 3C.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] The embodiments of this invention are described with reference toconsecutive layers (i.e., a photomask or reticle layer on a substrate),but these methods are applicable to any of the various material layers(described above) used to fabricate a semiconductor integrated circuit.

[0040] In the current application, the terms “semiconductive waferfragment” or “wafer fragment” or “wafer” will be understood to mean anyconstruction comprising semiconductor material, including but notlimited to bulk semiconductive materials such as a semiconductor wafer(either alone or in assemblies comprising other materials thereon), andsemiconductive material layers (either alone or in assemblies comprisingother materials). The term “substrate” refers to any supportingstructure including, but not limited to, the semiconductive waferfragments or wafers described above.

[0041] A conventional registration measurement structure comprises a“box-in-box” overlay structure (also called a “target” or “site”) thattypically comprises two or more overlay components (marks), andrepresents or describes the overlay of a given material layer withrespect to a previously deposited material layer at a single site (alsocalled a “point” or “location”) on a readable field of a wafer. Suchregistration measurement structures are repeated at various pointsacross the wafer. With respect to a box-in-box registration structure,significant information can be obtained at each site, for instance, bymeasuring or at least two different directions (e.g., in a typicalCartesian coordinate system, measuring in an “x” and a “y” direction).Information or data can be obtained in this manner across an entiresilicon wafer. This data can then be analyzed, modeled, or otherwisemanipulated so as to accomplish various tasks, such as, for example, toreduce or remove overlay error and achieve proper registration of asubsequently deposited layer with respect to previous layers. Suchoverlay error can be caused by certain tooling or IC fabricationprocesses.

[0042] Automatic metrology systems (not shown here) are typicallydesigned to accomplish swift, precise, and unattended registrationmeasurements of semiconductor features, including registrationmeasurement structures, for example, the box-in-box registrationstructure described herein. Such systems are programmable and include aspecialized imaging tool (e.g., an optical system), an autofocusmechanism (e.g., a laser focusing system), and a specialized opticalmicroscope, and are typically electronically-controlled. Oneregistration tool suitable for use with respect to the present inventionis an IVS registration tool (e.g., the IVS-120 optical metrology tool)available from Schlumberger Automated Test Equipment (ATE), located inSan Jose, Calif. The tool includes an adaptive RG software algorithmthat provides the capability to measure targets using images of thetargets that are created by the image sensing and optical apparatuses inthe registration tool. KLA-Tencor Corporation, located in San Jose,Calif., also manufacturers a variety of suitable registration softwarepackages, sold under the brand name KLASS™.

[0043] Registration tools can detect a position of overlay marks thatmake up, for example, a box-in-box registration structure on asubstrate. The registration tool typically images the substrate andregistration structure(s) using an optical system which can include aradiation source and a radiation detector (neither of which is shown) toproduce a registration signal that is processed by a processor (also notshown). Imaging of the registration structure on the substrate can beaccomplished by capturing two-dimensional or three-dimensional images ofthe registration structure using an image detector (not shown), such asa charge coupled device (CCD) camera so as to provide data of theregistration structure to the processor.

[0044] The electrical, mechanical and optical design of registrationtools are conventional and well known to those of skill in the art. Itwill be understood by those having skill in the art that the processorutilized in conjunction with the registration tool can comprise amicroprocessor, an Application-Specific Integrated Circuit (ASIC), orany other combination of hardware and or/or software. It will also beunderstood by those of skill in the art that the processor can bedesigned as part of an existing processor of a registration tool, oralternatively, as a stand-alone processor.

[0045] Registration is typically obtained by imaging registrationmeasurement structures generally comprising components (marks) on asubstrate. Exemplary substrates comprise silicon, silicon nitride,silicon dioxide, silicon carbide, gallium arsenide or othersemiconductor material. In general, the registration measurementstructure comprises a first component in a first or lower layer of asemiconductor construction, and a second component in an overlyingsecond or upper layer. The registration tool then typically determines,based on the image and/or reference points on the first component, therelative position of the second component of the registrationmeasurement structure. It then creates a signal based on that image orreference points.

[0046] Ideally, the second component is symmetrically positioned withrespect to the first component, and its center position is well defined.However, as described above, metal deposition processes can result in anasymmetric layer being deposited onto the first component of theregistration measurement structure, resulting in an inaccurate or falsemeasurement being taken of the registration structure. The falsemeasurement is then sent as a signal to the patterning apparatus, eventhough the second component itself may be symmetrically positioned. Dueto the registration error caused by the asymmetric film deposition onthe first component of the registration structure, it can be difficultto determine a center position of the second component.

[0047] Referring now to FIGS. 1A-1B, a first embodiment of the inventionis described with reference to a method of reducing registration errorcaused by asymmetrical deposition processes.

[0048] Referring to FIGS. 1A and 1B, top and cross-sectional views,respectively, of box-in-box registration measurement structure 1 areshown. A first component 2 comprising a larger box formed as raised areaor “mesa” in the shape of a square is formed over or in a substratelayer 10. Raised first component 2 comprises a top edge 11. A secondcomponent 4 comprising a smaller box comprising a photoresist layer isformed as a top layer 12 over the larger box 2 and substrate 10 tocorrespond with the first component 2. The photoresist layer cancomprise a variety of photosensitive polymeric materials for example, anovalac resin.

[0049] As shown in FIGS. 1A-1B and 2A-2B, the first component 2 of theregistration structure 1 can be a raised structure such as a mesa thatis formed in a substrate 10. As shown in FIG. 2C, the first component 2′can also be a recessed structure or trench etched into a substrate layer10′. The first component 2 can be formed to be about 1 to about 4microns (μm) wide, or more preferably, about 2 to about 4 microns (μm)wide. The height of the first component 2 is typically about 0.1 toabout 0.5 microns (λm) or more preferably about 0.3 to about 0.5 microns(μm). The above-described dimensions can vary widely depending on thespecific application and are provided by way of example only. Althoughdescribed as mesas (or trenches), it will be understood that the shapeof a registration measurement structure 1 can vary to conveniencedepending on the application at hand. For example, other suitable shapesfor the registration measurement structure can include crosses,chevrons, among others. The registration structure can be made accordingto well-known, conventional fabrication processes.

[0050] As shown in FIGS. 1A and 2A, the registration measurementstructure 1 is shown without a material layer (16) deposited over thefirst component 2 of the structure. The upper box (second component) 4appears to be in alignment (i.e., registration) with the lower box(first component) 2. When there is no asymmetric deposition of amaterial on the first component of the registration measurementstructure, distances such as height and width can be determined bymeasuring distances between edges (or other reference point) on theregistration measurement structure. Such distances are referred toherein as “critical dimensions”. For example, edges A through H of theregistration measurement structure can be perceived or recognized by animaging device, and thus measured, by a registration tool (not shown).As shown, the first component 2 of the registration structure comprisesfirst and second edges B and C, the second component 4 comprises firstand second edges D and E, and the asymmetric film layer comprises anedge A.

[0051] With respect to FIGS. 1A-1B, a registration structure that isfree of an asymmetrically deposited film (16) is shown. Registrationerror, if any, between the overlay of the upper box (second component) 4with respect to the lower box (first component) 2, can be obtained bydetermining the distance from edge C to edge D (referred to as “CD”) andthe distance from edge E to edge F, (referred to as “EF”). Thesedistances can be compared, and the error can be substantially accountedfor by the following subtraction one distance from the other, forexample, distance CD minus distance EF (i.e., CD-EF).

[0052] As shown in FIGS. 2A and 2B, metal deposition can result in anasymmetric layer 16 being deposited onto the first component (mesa) 2 ofregistration structure 1, and more specifically over certain portions ofits topography, e.g., the metal process films or layers deposited ontocertain edges of the first component (mesa) 2. For example, thedeposited film can be thicker on one side of the first component (mesa)2 than the other side.

[0053] Registration tools typically measure the registration structurefrom an edge to a centerline (or vice versa). A metal film 16 istypically deposited downwardly and at angle onto the substrate, in a setdirection such as from left to right across the surface, or in radialfashion.

[0054] A deposited metal film 16 generally appears opaque to the imagingmechanism of a registration tool. As such, the registration tool cannotdetect the true edges of the registration structure 2 through the opaquefilm, but images or measures the apparent edges of the registrationstructure 2 that includes an overlying film layer 16. One result of thisis that the perceived (i.e., measured) edges A, C, D, E, F and Hmeasured by a registration tool can be effectively offset by an amountcorresponding to the thickness (width) of the film layer 16 as measuredfrom edge A to edge B, which is contiguous to a reference edge (C) ofthe first component (trench, mesa) 2 of the registration structure.

[0055] The registration tool images and transmits a registration signalof the registration structure 1 to a processor (not shown), with theregistration signal including the offset amount due to the asymmetricdeposition of the film layer 16. As a result of the inclusion of theoffset amount in the registration image and signals, a subsequentlydeposited material layer (not shown), can be misaligned with respect toan underlying material layer.

[0056] As shown in FIGS. 2A and 2B, the first component (raised area ormesa) 2, is defined, at least in part, by edges B, C, G and H. As shown,the second component 4, exemplified by a photoresist layer, is formedonto a film layer 16 (e.g., metal) that has been asymmetricallydeposited over the first component 2. The second component 4 is defined,at least in part, by edges D and E. As shown, the deposition of the filmlayer 16 can result in a build-up of material along one side of thefirst component 2. This forms asymmetric deposition edges “A” and “F”,which are edges of the deposited material 16 that is contiguous withedges B and G of the first component.

[0057] Here, certain edges of the registration measurement structure(box-in-box) can be perceived or recognized, and thus measured, by aregistration tool (not shown). As shown in FIGS. 2A-2B, measurable edgesinclude asymmetric deposition edges A and F, and edges C, D, E, and H ofthe first and second components of the registration measurementstructure. Edges B and G of the first component 2 of the registrationstructure, however, cannot be perceived or measured using theregistration tool due to the generally opaque asymmetric film layer 16that is deposited over these edges.

[0058] Thus, using a registration tool to determine the alignment of thesecond component 4 of a registration structure comprising anasymmetrically deposited film layer 16, can result in an erroneous orfalse registration measurement. The amount of the false registrationmeasurement corresponds to the thickness of the asymmetric layer 16contiguous to the edge B of the first component 2 of the registrationstructure, which can be represented by the distance from edge A of theasymmetric layer 16 to edge B of the first component 2 (i.e., distanceAB), or alternatively—because of structure symmetry—the distance betweenedges F and G of the asymmetric layer 16 and the first component 2 ofthe second depicted registration structure (i.e., distance FG).

[0059] The width of the first component 2, or simply the criticaldimension AC, can be obtained according to the known (or predetermined)dimensions of the pattern (e.g., mask or reticle) used in forming thefirst component 2. Dimension AC can also be determined by measuringand/or experimental sampling of registration structure components usingmethods known to those of skill in the art. Such critical dimensions canbe measured using a registration tool or Critical Dimension ScanningElectron Microscope. As a practical matter, such a determination candesirably take place prior to asymmetric deposition of the metal layer.Measuring critical dimensions introduces error into the final overlay ofone material layer to a subsequent material layer. However, such erroris significantly less than the error that typically would result if theerror due to asymmetric film deposition is not accounted for (i.e., theerror to asymmetric film deposition is assumed to be negligible orzero).

[0060] Using the measurement data obtained above (i.e., the apparentregistration error and critical dimensions AC and AB), the true oractual registration error due to asymmetric deposition (or amount of theregistration offset corresponding to the thickness of the asymmetricdeposition on the edge of the first component of the registrationstructure) can be calculated. By way of example, in the box-in-boxregistration structure illustrated, the registration error due toasymmetric deposition of the film layer 16 can be calculated as thedifference between the magnitude of critical dimension (distance) AC andthe magnitude of critical dimension (distance) BC, or simply, distanceAC minus distance BC (i.e., AC−BC). This, of course, corresponds to thedistance AB. Since the box-in-box registration measurement structure 1that is shown is itself symmetrical, the offset or overlay error of thesecond component 4 relative to the first component 2 is equal to halfthe magnitude of the critical dimension (distance) BC (i.e., BC/2).

[0061] With the registration error due to asymmetric deposition havingbeen determined, an actual registration value for the registrationmeasurement structure 1 comprising an asymmetric deposition layer 16 canbe determined. This actual value can be conveyed to a patterningapparatus to align a subsequent layer onto the substrate.

[0062] The amount of asymmetric deposition corresponding to thethickness of the deposition layer 16, can vary across the surface of thesubstrate. As such, the amount of asymmetric deposition is preferablymeasured, modeled and corrected for at each registration measurementstructure (e.g., the box-in-box registration structure illustrated inhere) across the wafer. That is, each structure 1, and eachcorresponding error determination, can be considered as a point. Thisprocess can be continuing, point-by-point, across a substrate. Thepoints can be collected to create a data set. From this data set, anoverall alignment error for overlying patterned layers of an IC can bedetermined and/or modeled, and overall alignment of the layers can beachieved.

[0063] A key feature of this invention is that the critical dimensiondeterminations are utilized to obtain an error or offset amount due toasymmetric film deposition. The offset amount can be conveyed to apatterning apparatus. Such error can be effectively subtracted out of orremoved from the overall registration for a structure and, by continuingthe process, across a wafer substrate.

[0064] As depicted in FIG. 2C, in another embodiment, the registrationmeasurement structure 1′ can comprise a first component 2′ in the formof a recessed structure of trench. As shown, a film layer 16′ has beenasymmetrically deposited over the edge B′ of the trench-structured firstcomponent 2′. Measurements can be taken with respect to edges A′ throughH′ of the registration measurement structure 1′ to determine and resolvethe registration error in the alignment of the first and secondcomponents 2′, 4′, according to the method as described with respect toFIGS. 2A-2B.

[0065] Referring now to FIGS. 3A-3C, a second embodiment of a methodaccording to the invention is described with reference to imaging a pairof gate images of a reference measurement structure to provide forimproved site registration, or reduced (and potentially eliminated)registration error caused by asymmetrical deposition processes. Again,when a film layer (metal material) 16 is deposited onto a wafersubstrate, for example, to create metal interconnects or other ICelements, components (which can, alone or in combination with othercomponents, make up a registration measurement structure) are used toaccomplish registration.

[0066] The true or actual centerline of the exemplary box-in-boxregistration structure 1″ is indicated by solid line 30″. The depositionof the material layer 16″ can cause mis-registration between the outerbox component 2″ and the inner box component 4″, which ultimately canresult in the misalignment of overlying patterned layers by the amountby which the perceived or apparent site line is offset from the actualor true centerline 30″ of the registration structure.

[0067] Still referring to FIGS. 3A-3B, left and right image gates X₁,X₂, are shown to overlie the first component 2″ comprising a raised,larger outer box, of the registration structure 1″. Image gates Y₁ andY₂ are shown to overlie edges D″ and E″ of the second component 2″comprising the second component 4″ comprising an inner, smaller boxcomprising, for example, a photoresist layer. A registration tool usesimage gates X₁, X₂, Y₁ and Y₂ to determine where the centerline 30″ ofthe outer and inner boxes 2″, 4″ of the registration structure 1″ arelocated. A registration tool can be used to obtain the gate images bytaking a contrast images (e.g., a CCD photograph).

[0068] As depicted, the registration measurement structure 1″ comprisesa first component (mark) 2″, which is formed in a lower substrate layer10″ using standard IC fabrication techniques, such as resist pattern andetch. The registration measurement structure 1″ further comprises asecond component (mark) 4″ as a top or current layer, shown here as aphotoresist layer. The first and second components 2″, 4″ are shown asidentical or substantially identical in shape (i.e., as rectangles),thereby creating a symmetrical box-in-box design. Thus, an exemplary“ideal” registration measurement structure 1″ is shown. It will berecognized and understood by those of skill in the art that theregistration structure can be fabricated using known but imperfectmanufacturing processes, which lead to imperfections in its shape.

[0069] Referring to FIGS. 3C-3E, enlarged schematic images (referred toherein as “gate images”) of registration structure 1″ comprising theouter box (first component) portions 2 a″, 2 b″, and asymmetricallydeposited film layer portions 16 a″ and 16 b″ are illustrated. Morespecifically, a pair of gate images I₁ and I₂ (as shown, left and right)can be used to determine the position of sides or edges of theillustrated box-in-box registration measurement structure.

[0070] As illustrated in FIG. 3C, asymmetric film deposition layerportions 16 a″, 16 b″ cause the registration tool to image the apparentcenterline of outer box portion 2 a″ with deposition layer portion 16 a″thereon as an offset line 31″, and the apparent centerline of outer boxportion 2 b″ with deposition layer portion 16 a″ thereon as an offsetline 32″.

[0071] This, in turn, registers the apparent centerline of the overallbox-in-box structure 1″ (i.e. site center) as an offset or site line33″.

[0072] The registration tool accomplishes this determination by imaginga pair of images I₁ and I₂ of the outer box (first) component 2″ of theregistration structure, and determining a value of the apparentcenterlines of each of the images I₁ and I₂ of the first material layeror component 2″. The image centerline values are then averaged toprovide a site line 33″, or first offset centerline value. A pair ofimages delineated by the image gates Y₁ and Y₂ (not depicted) are alsotaken of the inner box (second) component 4″ of the registrationstructure, and a value of the apparent centerlines of each of the imagesof the second material layer or component 4″ are determined. The imagecenterline values of the second material layer images are then averagedto provide a second offset centerline value. The first offset centerlinevalue is then compared with the second offset centerline value toprovide a first delta value (Δ₁), referred to as “site-induced-shift”.Such registration measurements can be taken for each registrationstructure 1″ across a wafer, and a data set created.

[0073] In a next step, the registration tool can electronically rotateor flip one or both of the gate images I₁, I₂ of the portions of theouter box components 2 a″, 2 b″, resulting in the image pairs shown inFIGS. 3D and 3E.

[0074] As illustrated in FIG. 3D, both gate images I₁, I₂ have beenelectronically flipped by the registration tool, resulting in flippedimages I_(1F), I_(2F). As shown, each of the images have been flipped180° about a central axis 40 a″, 40 b″ (FIGS. 3A-3B) of the image gates.Once flipped, the registration tool measures the apparent centerlines34″ and 35″, respectively, of the outer box components 2 a″, 2 b″ so asto determine the amounts that the apparent centerlines 34″ and 35″ areoffset from the true centerline 30″. The image centerline values 34″,35″ of the flipped images I_(1F), I_(2F), of the first material layer orcomponent 2″ are then determined and averaged to provide a site line36″, or third offset centerline value. The third offset center linevalue is then compared to the second offset centerline value to providea second delta value (Δ₂).

[0075] The Δ₁ value is then subtracted from the Δ₂ value to provide aΔ_(s) value, which is then averaged to provide a registrationmeasurement error, which corresponds to the offset amount due to theasymmetric deposition of the film layer portions 16 a″, 16 b″. Ingeneral, the greater the averages Δ_(s) value, the greater the asymmetryof the film layer over the outer box component portions 2 a″, 2 b″. Theregistration measurement error is then subtracted from the registrationstructure centerline value to generate a corrected data representativeof an actual centerline value of the registration structure. The actualcenterline value of the registration structure is then conveyed to apatterning apparatus to align a subsequently patterned layer.

[0076] Typically the sputter (or other metal deposition process) tool(not shown) applies the metal or other material layer in a manner thatintroduces a radial asymmetry to the deposited film layer 16″. In otherwords, for a registration structure 1″ in which the first component 2″comprises a raised feature, an excess amount of material can bedeposited onto one side of the wafer substrate resulting in a build-upof material along one side of the lower component 2″ of a registrationmark. When a registration tool then measures the field (i.e., oneexposure from the exposure tool), the position of the raised feature 2″appears to be closer toward the wafer center than its actual position.Alternatively, if the lower component 2″ comprises a trench, theposition of the recessed feature 2″ appears to be farther from the wafercenter than its actual position. This phenomena is called “wafermagnification.” Wafer magnification can be corrected or accounted for byentering a wafer magnification factor into the exposure tool to changethe exposure tool stepping distance between field images.

[0077] In another embodiment of a method according to the invention,only one of two gate images (e.g., I₁ or I₂) is electronically rotatedor flipped onto itself, as shown in FIGS. 3C and 3E. As shown, 12 (FIG.3C) has been flipped to obtain flipped image I_(2F), as depicted in FIG.3E.

[0078] According to the method, a pair of images I₁, I₂ of the outer box(first component) 2″ of the registration structure 1″ are again obtained(FIG. 3C), and an image centerline value 37″, 38″ for each of the imagesI₁, I₂ is determined and averaged to provide a first offset centerlinevalue.

[0079] A pair of images delineated by the image gates Y₁ and Y₂ (FIG.3A) are also again taken of the inner box (second) component 4″ of theregistration structure, and a value of the apparent centerlines of eachof the images of the second material layer or component 4″ aredetermined and averaged to provide a second offset centerline value. Thefirst and second offset centerline values are then compared to provide afirst delta value (Δ₁).

[0080] One of the images, here image I₂ of the outer box (first)component 2″ has been flipped/rotated resulting in a flipped imageI_(2F) and a non-flipped image I₁, as shown in FIG. 3E. Once rotated orflipped, the registration tool can measure the respective apparentcenterlines, 37″ and 38″ of the flipped image I_(2F) and a non-flippedimage II of the outer box component portions 2 a″, 2 b″, and average thevalues to provide a site line 39″, or third offset centerline value. Thethird offset center line value is then compared to the second offsetcenterline value to provide a second delta value (Δ₂). The Δ₁ value isthen subtracted from the Δ₂ value to provide a Δ_(s) value whichcorresponds to a registration measurement error due to the asymmetricdeposition of the film layer portions 16 a″, 16 b″. The registrationmeasurement error is then subtracted from the registration structurecenterline value to generate a corrected data representative of anactual centerline value of the registration structure. The actualcenterline value is then conveyed to a patterning apparatus to align asubsequently patterned layer relative to the registration structure andthe component 4″.

[0081] One problem that can result from rotating only one of the gateimages is the phenomenon of field magnification. Field magnificationresults when the image-sensing mechanism or apparatus magnifies a fieldcomprising a plurality of registration structures or sites. Fieldmagnification can be corrected or accounted for by a field magnificationfactor that can be entered into the exposure tool to reduce or increasethe field magnification as needed.

[0082] In accordance with the present method, to eliminate such errorsdue to rotation of gate images (e.g., wafer magnification, fieldmagnification, and translational shifts) and to account as well for theerror associated with asymmetric film deposition, two measurements aretaken. First, non-flipped gate image measurements are taken. Then, etherone gate image (e.g., I₁, or I₂) is flipped and measured, or both gateimages (e.g., I₁ and I₂) are flipped and measured.

[0083] In another embodiment of this method, a pair of images I₁, I₂ ofthe outer box (first component 2″) are obtained (FIG. 3C), and one ofthe pair of images is manipulated resulting in a first flipped image anda non-flipped image. Apparent image centerline values of the flipped andnon-flipped images are determined and averaged to provide a first offsetcenterline value. A pair of images of the inner box (second component)4″ of the registration structure 1″ are then obtained as describedherein, and apparent image centerline values of each of the images ofthe inner box component) 4″ are then determined and averaged to providea second offset centerline value. The first and second offset centerlinevalues are then compared to provide a first delta value (Δ₁).

[0084] The other (non-flipped) image of the outer box component 2″ isthen flipped/rotated to provide a pair of flipped gate images I_(1F),I_(2F), and the image centerline values of the flipped images aredetermined and averaged to provide a third offset centerline value. Thethird offset centerline value is then compared to the second offsetcenterline value to provide a second delta value (Δ₂). The Δ1 value isthen subtracted from the Δ₂ value to provide a Δ_(s) value correspondingto a registration measurement error, which is then subtracted from theregistration structure centerline value to generate a corrected datarepresentative of an actual centerline value of the registrationstructure. This actual centerline value of the registration structurecan then be electronically transmitted to a patterning apparatus toalign a subsequently patterned layer relative to the registrationstructure.

[0085] The present layer-to-layer overlay metrology can be used tomeasure the alignment accuracy between a photoresist layer and anunderlying substrate layer, and also to determine the alignment accuracyof a photoresist mask for etching a substrate material and, ifnecessary, the photoresist can be removed or reworked.

[0086] It will be understood that the foregoing methods of the inventioncan be implemented by automated registration tools comprising computerprogram instructions and/or algorithms programmed therein. Thesecomputer program algorithms can be provided to a processor (not shown)or other programmable data processing apparatus to produce a machine,such that the instructions that execute on the processor or otherprogrammable data processing apparatus create means for implementing thefunctions specified in the methods. These computer program instructionscan also be stored in a computer-readable memory that can direct aprocessor or other programmable data processing apparatus to function ina particular manner, such that the instructions stored in thecomputer-readable memory produce an article of manufacture includinginstruction means which implement the functions specified in themethods.

[0087] Accordingly, the methods and illustrations provided hereinsupport combinations of means of performing the specified functions,combinations of steps (i.e., one such combination comprising a singlestep, another such combination comprising two or more steps) forperforming the specified functions and program instruction means forperforming the specified functions. It will also be understood that eachmethod can be implemented by special purpose hardware-based systems,such as the kind described above or other conventional systems, whichcan perform the specified functions or steps as described above and/orby combinations of special purpose hardware and computer instructions.

[0088] Overlay metrology is performed to determine how well one layeroverlays to a previous layer. Thus, metrology compares a registrationmark, generally referred to as a metrology mark, on a current layer withan registration mark on a previous layer. The registration or metrologytool detects the registration marks and determines the positions of thecurrent and previous registration marks. From these positions, anoverlay offset can be calculated. Accordingly, the present invention canbe used to detect the positions of the current and previous overlaymarks during the metrology phase.

[0089] While the present invention is described in the context of metaldeposition processes, such as sputtering, it will be understood that theinvention can apply to any film that can be deposited to have a varyingthickness from one side of a feature (e.g., a transoral line, a pattern,etc.), or, from the center to the edge of, for example, a wafer.

[0090] The present invention has been described in terms of thepreferred embodiments, and it is recognized that equivalents,alternatives, and modifications, aside from those expressly stated, arepossible and within the scope of the appending claims.

1. A method for reducing registration measurement error due to anasymmetrically deposited film using critical dimensions, the methodcomprising: providing a semiconductor registration structure in at leasttwo overlying material layers of a semiconductor wafer for registeringthe relative position of a first material layer to a second materiallayer; determining a first critical dimension of the registrationstructure; determining an apparent registration measurement of theregistration structure; measuring a second critical dimension of theregistration structure when the registration structure comprises anasymmetrically deposited film; using the first critical dimension andthe second critical dimension to determine the registration measurementerror of the registration structure due to the asymmetrically-depositedfilm; subtracting the registration measurement error from the apparentregistration measurement of the registration structure to generate acorrected data representative of an actual registration of theregistration structure; conveying the actual registration data to apatterning apparatus to align a subsequently patterned layer relative tothe structure.
 2. The method of claim 1 wherein step of determining thefirst critical dimensions comprises measuring the registration structureprior to deposition of the asymmetric film onto the structure.
 3. Themethod of claim 1 wherein the step of determining the first criticaldimension comprises an experimental sampling of registration components.4. The method of claim 1 wherein the first and second material layerscomprise any two consecutive material layers on a semiconductorintegrated circuit.
 5. The method of claim 1 wherein the first materiallayer comprises a semiconductive material, and the second material layercomprises a photoresist film.
 6. The method of claim 1 wherein theregistration structure comprises a box-in-box alignment structure.
 7. Amethod for reducing registration measurement error due to anasymmetrically deposited film using critical dimensions, the methodcomprising: providing a registration measurement structure formed inoverlying upper and lower layers of a semiconductor construction, thelower layer comprising a first component of the registration measurementstructure, and the upper layer comprising a second component of theregistration measurement structure, the first component comprising afirst edge and a second edge, and a first distance from the first edgeto the second edge, and the second component comprising a first edge anda second edge; acquiring data from the first component of theregistration measurement structure to provide a first critical distancevalue from the first edge to the second edge; acquiring data from theposition of the first component in relation to the second component toprovide an apparent registration measurement; acquiring data from thefirst component having an asymmetrical film layer deposited thereon, toprovide a second critical distance value from the first edge of thefirst component to an edge of the film layer disposed contiguously tothe first edge of the first component; comparing the second distancevalue to the first distance value to generate an alignment error valuecorresponding to a third distance value measured from said edge of thefilm layer to the second edge of the first component; comparing theapparent registration measurement and the third distance value to removethe alignment error and generate an actual registration value; andconveying the actual registration value to a patterning apparatus foraligning a subsequent layer to the structure.
 8. A computer readablemedium on a computer, the computer readable medium comprising computerexecutable instructions for performing a method comprising: determininga first critical dimension of a registration structure, thesemiconductor registration structure formed in at least two overlyingmaterial layers of a semiconductor wafer for registering the relativeposition of a first material layer to a second material layer;determining an apparent registration measurement of the registrationstructure; measuring a second critical dimension of the registrationstructure when the registration structure comprises an asymmetricallydeposited film; using the first critical dimension and the secondcritical dimension to determine the registration measurement error ofthe registration structure due to the asymmetrically-deposited film;subtracting the registration measurement error from the apparentregistration measurement of the registration structure to generate acorrected data representative of an actual registration of theregistration structure; conveying the actual registration data to apatterning apparatus to align a subsequently patterned layer relative tothe structure.
 9. A registration system, comprising: a registrationmeasurement structure disposed within overlying layers of asemiconductor construction, a first component of the registrationmeasurement structure disposed within a first layer of the semiconductorconstruction and comprising first and second edges and a distancetherebetween, and a second component of the registration measurementstructure disposed within a first layer of the semiconductorconstruction and comprising first and second edges; a registrationapparatus operable for acquiring image data of i) the first and secondedges of the first component; ii) the first and second edges of thesecond component; iii) an edge of a film layer asymmetrically depositedonto the second edge of the first component; and iv) the first or secondedge of the first component in relation to the first edge of the secondcomponent; a processor operable for producing distance values betweensaid edges from the acquired image data, the distance values comprising:i) a first distance measured from the first edge to the second edge ofthe first component; and ii) a second distance measured from the firstedge of the first component to the edge of the asymmetrically depositedfilm layer; the processor further operable for producing an apparentregistration measurement of the first component in relation to thesecond component based on measurements of the first or second edge ofthe first component to the first edge of the second component; theprocessor further operable for comparing the second distance value tothe first distance value to generate an alignment error valuecorresponding to a third distance between the edge of the asymmetricallydeposited film layer and the second edge of the first component; theprocessor further operable for comparing the apparent registrationmeasurement and the alignment error value to generate an actualregistration value corresponding to the position of the second componentrelative to the first component; the processor further operable toconvey the actual registration value to a patterning apparatus foraligning a subsequent layer to the registration measurement structure.10. A method for reducing asymmetrically deposited film inducedregistration error, the method comprising: providing a semiconductorregistration structure for registering the relative position of a firstmaterial layer to the relative position of a second material layer in asemiconductor wafer, the registration structure comprising a centerlinevalue; obtaining a pair of images of the first material layer of theregistration structure; determining an image centerline value of each ofthe images of the first material layer; averaging the image centerlinevalues of the first material layer images to provide a first offsetcenterline value; obtaining a pair of images of the second materiallayer of the registration structure; determining an image centerlinevalue of each of the images of the second material layer; averaging theimage centerline values of the second material layer images to provide asecond offset centerline value; comparing the first offset centerlinevalue with a second offset centerline value to provide a first deltavalue (Δ₁); manipulating the pair of images of the first material layerto obtain flipped images of the first material layer; determining animage centerline value of each of the flipped images of the firstmaterial layer; averaging the image centerline values of the firstmaterial layer flipped images to provide a third offset centerlinevalue; comparing the third offset centerline value to the second offsetcenterline value to provide a second delta value (Δ₂); subtracting theΔ₁ value from the Δ₂ value to provide a Δ_(s) value, and averaging theΔ_(s) value to provide a registration measurement error; subtracting theregistration measurement error from the registration structurecenterline value to generate a corrected data representative of anactual centerline value of the registration structure; and conveying theactual centerline value of the registration structure to a patterningapparatus to align a subsequently patterned layer relative to theregistration structure.
 11. A computer readable medium on a computer,the computer readable medium comprising computer executable instructionsfor performing the method of claim
 10. 12. A method for reducingasymmetrically deposited film induced registration error, the methodcomprising: providing a semiconductor registration structure forregistering the relative position of a first material layer to therelative position of a second material layer in a semiconductor wafer,the registration structure comprising a centerline value; obtaining apair of images of the first material layer of the registrationstructure; determining an image centerline value of each of the imagesof the first material layer; averaging the image centerline values ofthe first material layer images to provide a first offset centerlinevalue; obtaining a pair of images of the second material layer of theregistration structure; determining an image centerline value of each ofthe images of the second material layer; averaging the image centerlinevalues of the second material layer images to provide a second offsetcenterline value; comparing the first offset centerline value with asecond offset centerline value to provide a first delta value (Δ₁);manipulating one of the pair of images of the first material layerresulting in a flipped image and a non-flipped image of the firstmaterial layer; determining an image centerline value of the flippedimage and the non-flipped image of the first material layer; averagingthe image centerline values of the flipped image and the non-flippedimage of the first material layer to provide a third offset centerlinevalue; comparing the third offset centerline value to the second offsetcenterline value to provide a second delta value (Δ₂); subtracting theΔ₁ value from the Δ₂ value to provide a Δ_(s) value corresponding to aregistration measurement error; subtracting the registration measurementerror from the registration structure centerline value to generate acorrected data representative of an actual centerline value of theregistration structure; and conveying the actual centerline value of theregistration structure to a patterning apparatus to align a subsequentlypatterned layer relative to the registration structure.
 13. A computerreadable medium on a computer, the computer readable medium comprisingcomputer executable instructions for performing the method of claim 12.14. A method for reducing asymmetrically deposited film inducedregistration error, the method comprising: providing a semiconductorregistration structure for registering the relative position of a firstmaterial layer to the relative position of a second material layer in asemiconductor wafer, the registration structure comprising a centerlinevalue; obtaining a pair of images of the first material layer of theregistration structure; manipulating one of the pair of images of thefirst material layer resulting in a first flipped image and anon-flipped image of the first material layer; determining an imagecenterline value of the first flipped image and the non-flipped image ofthe first material layer; averaging the image centerline values of thefirst flipped image and the non-flipped image of the first materiallayer to provide a first offset centerline value; obtaining a pair ofimages of the second material layer of the registration structure;determining an image centerline value of each of the images of thesecond material layer; averaging the image centerline values of thesecond material layer images to provide a second offset centerlinevalue; comparing the first offset center line value with a second offsetcenterline value to provide a first delta value (Δ₁); manipulating asecond of the pair of images of the first material layer resulting infirst and second flipped images of the first material layer; determiningan image centerline value of the second flipped image of the firstmaterial layer; averaging the image centerline values of the first andsecond flipped images to provide a third offset centerline value;comparing the third offset center line value to the second offsetcenterline value to provide a second delta value (Δ₂); subtracting theΔ₁ value from the Δ₂ value to provide a Δ_(s) value corresponding to aregistration measurement error; subtracting the registration measurementerror from the registration structure centerline value to generate acorrected data representative of an actual centerline value of theregistration structure; and conveying the actual centerline value of theregistration structure to a patterning apparatus to align a subsequentlypatterned layer relative to the registration structure.
 15. A computerreadable medium on a computer, the computer readable medium comprisingcomputer executable instructions for performing the method of claim 14.16. A method for reducing registration error in a semiconductor device,the method comprising: obtaining a pair of images representative of aregistration structure that comprises an asymmetric deposition layer;measuring the pair of images; flipping the pair of images to obtainflipped images; measuring the flipped images; comparing the pair ofimages to the flipped images to obtain an amount corresponding to thedifference between the images and flipped images; removing thedifference so as to obtain a true site offset; and conveying the truesite offset to a patterning apparatus to align a subsequently patternedlayer relative to the registration structure.
 17. A method forcountering registration site structure film induced registration errorin semiconductor devices, the method comprising: forming a registrationstructure for the alignment of at least two overlying material layers ofa semiconductor device, the registration structure comprising anasymmetric deposition layer; obtaining two non-flipped images of theregistration structure; flipping both of the images to obtain flippedimages; comparing the non-flipped images to the flipped images to obtainan amount corresponding to the difference between the non-flipped andflipped images; and using the difference to obtain a true structureoffset; conveying the true structure offset to a patterning apparatus toalign a subsequently patterned layer relative to the registrationstructure.
 18. A method for countering registration site asymmetric filminduced registration error, the method comprising: providing anon-uniform registration site comprising an asymmetric deposition layerfor the alignment of two or more material layers in an integratedcircuit; obtaining at least two non-flipped images of a non-uniformregistration site; flipping one of the two images to obtain a flippedimage; comparing the non-flipped image to the flipped image to determinethe difference between the non-flipped and flipped images so as toobtain a true registration site offset; and using the true site offsetto counter registration site asymmetric film induced registration errorby conveying the true site offset to a patterning apparatus to align asubsequently patterned layer relative to the registration site.
 19. Asystem for reducing registration measurement error caused by asymmetricfilm deposition, the system comprising: means for determining a firstcritical dimension of the registration structure, the registrationstructure formed in at least two overlying material layers of asemiconductor wafer for registering the relative position of a firstmaterial layer to a second material layer; means for determining anapparent registration measurement of the registration structure; meansfor measuring a second critical dimension of the registration structurewhen the registration structure comprises an asymmetrically depositedfilm; means for using the first critical dimension and the secondcritical dimension to determine the registration measurement error ofthe registration structure due to the asymmetrically-deposited film;means for subtracting the registration measurement error from theapparent registration measurement of the registration structure togenerate a corrected data representative of an actual registration ofthe registration structure; means for conveying the actual registrationdata to a patterning apparatus to align a subsequently patterned layerrelative to the structure.
 20. A computer programmed product forreducing registration measurement error using critical dimensions, thecomputer program product comprising a computer readable storage mediumhaving a computer-readable program code means embodied in the medium,the computer-readable program code means comprising: computer-readableprogram code for determining a first critical dimension of aregistration structure, the semiconductor registration structure formedin at least two overlying material layers of a semiconductor wafer forregistering the relative position of a first material layer to a secondmaterial layer; computer-readable program code for determining anapparent registration measurement of the registration structure;computer-readable program code for measuring a second critical dimensionof the registration structure when the registration structure comprisesan asymmetrically deposited film; computer-readable program code forusing the first critical dimension and the second critical dimension todetermine the registration measurement error of the registrationstructure due to the asymmetrically-deposited film; computer-readableprogram code for subtracting the registration measurement error from theapparent registration measurement of the registration structure togenerate a corrected data representative of an actual registration ofthe registration structure; computer-readable program code for conveyingthe actual registration data to a patterning apparatus to align asubsequently patterned layer relative to the structure.
 21. Aregistration system, comprising: means for providing a semiconductorregistration structure for registering the relative position of a firstmaterial layer to the relative position of a second material layer in asemiconductor wafer, the registration structure comprising a centerlinevalue; means for obtaining a pair of images of the first material layerof the registration structure; means for determining an image centerlinevalue of each of the images of the first material layer; means foraveraging the image centerline values of the first material layer imagesto provide a first offset centerline value; means for obtaining a pairof images of the second material layer of the registration structure;means for determining an image centerline value of each of the images ofthe second material layer; means for averaging the image centerlinevalues of the second material layer images to provide a second offsetcenterline value; means for comparing the first offset centerline valuewith a second offset centerline value to provide a first delta value(Δ₁); means for manipulating the pair of images of the first materiallayer to obtain flipped images of the first material layer; means fordetermining an image centerline value of each of the flipped images ofthe first material layer; means for averaging the image centerlinevalues of the first material layer flipped images to provide a thirdoffset centerline value; means for comparing the third offset centerlinevalue to the second offset centerline value to provide a second deltavalue (Δ₂); means for subtracting the Δ₁ value from the Δ₂ value toprovide a Δ_(s) value, and averaging the Δ_(s) value to provide aregistration measurement error; means for subtracting the registrationmeasurement error from the registration structure centerline value togenerate a corrected data representative of an actual centerline valueof the registration structure; and means for conveying the actualcenterline value of the registration structure to a patterning apparatusto align a subsequently patterned layer relative to the registrationstructure.
 22. A computer programmed product for reducing registrationmeasurement error using critical dimensions, the computer programproduct comprising a computer readable storage medium having acomputer-readable program code means embodied in the medium, thecomputer-readable program code means comprising: computer-readableprogram code for obtaining a pair of images of the first material layerof a semiconductor registration structure, the semiconductorregistration structure for registering the relative position of a firstmaterial layer to the relative position of a second material layer in asemiconductor wafer, the registration structure comprising a centerlinevalue; computer-readable program code for determining an imagecenterline value of each of the images of the first material layer;computer-readable program code for averaging the image centerline valuesof the first material layer images to provide a first offset centerlinevalue; computer-readable program code for obtaining a pair of images ofthe second material layer of the registration structure;computer-readable program code for determining an image centerline valueof each of the images of the second material layer; computer-readableprogram code for averaging the image centerline values of the secondmaterial layer images to provide a second offset centerline value;computer-readable program code for comparing the first offset centerlinevalue with a second offset centerline value to provide a first deltavalue (Δ₁); computer-readable program code for manipulating one of thepair of images of the first material layer resulting in a flipped imageand a non-flipped image of the first material layer; computer-readableprogram code for determining an image centerline value of the flippedimage and the non-flipped image of the first material layer;computer-readable program code for averaging the image centerline valuesof the flipped image and the non-flipped image of the first materiallayer to provide a third offset centerline value; computer-readableprogram code for comparing the third offset centerline value to thesecond offset centerline value to provide a second delta value (Δ₂);computer-readable program code for subtracting the Δ₁ value from the Δ₂value to provide a Δ_(s) value corresponding to a registrationmeasurement error; computer-readable program code for subtracting theregistration measurement error from the registration structurecenterline value to generate a corrected data representative of anactual centerline value of the registration structure; andcomputer-readable program code for conveying the actual centerline valueof the registration structure to a patterning apparatus to align asubsequently patterned layer relative to the registration structure. 23.A registration system comprising: means for providing a semiconductorregistration structure for registering the relative position of a firstmaterial layer to the relative position of a second material layer in asemiconductor wafer, the registration structure comprising a centerlinevalue; means for obtaining a pair of images of the first material layerof the registration structure; means for determining an image centerlinevalue of each of the images of the first material layer; means foraveraging the image centerline values of the first material layer imagesto provide a first offset centerline value; means for obtaining a pairof images of the second material layer of the registration structure;means for determining an image centerline value of each of the images ofthe second material layer; means for averaging the image centerlinevalues of the second material layer images to provide a second offsetcenterline value; means for comparing the first offset centerline valuewith a second offset centerline value to provide a first delta value(Δ₁); means for manipulating one of the pair of images of the firstmaterial layer resulting in a flipped image and a non-flipped image ofthe first material layer; means for determining an image centerlinevalue of the flipped image and the non-flipped image of the firstmaterial layer; means for averaging the image centerline values of theflipped image and the non-flipped image of the first material layer toprovide a third offset centerline value; means for comparing the thirdoffset centerline value to the second offset centerline value to providea second delta value (Δ₂); means for subtracting the Δ₁ value from theΔ₂ value to provide a Δ_(s) value corresponding to a registrationmeasurement error; means for subtracting the registration measurementerror from the registration structure centerline value to generate acorrected data representative of an actual centerline value of theregistration structure; and means for conveying the actual centerlinevalue of the registration structure to a patterning apparatus to align asubsequently patterned layer relative to the registration structure. 24.A computer programmed product for reducing registration measurementerror using critical dimensions, the computer program product comprisinga computer readable storage medium having a computer-readable programcode means embodied in the medium, the computer-readable program codemeans comprising: computer-readable program code for obtaining a pair ofimages of the first material layer of a registration structure, theregistration structure for registering the relative position of a firstmaterial layer to the relative position of a second material layer in asemiconductor wafer, the registration structure comprising a centerlinevalue; computer-readable program code for manipulating one of the pairof images of the first material layer resulting in a first flipped imageand a non-flipped image of the first material layer; computer-readableprogram code for determining an image centerline value of the firstflipped image and the non-flipped image of the first material layer;computer-readable program code for averaging the image centerline valuesof the first flipped image and the non-flipped image of the firstmaterial layer to provide a first offset centerline value;computer-readable program code for obtaining a pair of images of thesecond material layer of the registration structure; computer-readableprogram code for determining an image centerline value of each of theimages of the second material layer; computer-readable program code foraveraging the image centerline values of the second material layerimages to provide a second offset centerline value; computer-readableprogram code for comparing the first offset center line value with asecond offset centerline value to provide a first delta value (Δ₁);computer-readable program code for manipulating a second of the pair ofimages of the first material layer resulting in first and second flippedimages of the first material layer; computer-readable program code fordetermining an image centerline value of the second flipped image of thefirst material layer; computer-readable program code for averaging theimage centerline values of the first and second flipped images toprovide a third offset centerline value; computer-readable program codefor comparing the third offset center line value to the second offsetcenterline value to provide a second delta value (Δ₂); computer-readableprogram code for subtracting the Δ₁ value from the Δ₂ value to provide aΔ_(s) value corresponding to a registration measurement error;computer-readable program code for subtracting the registrationmeasurement error from the registration structure centerline value togenerate a corrected data representative of an actual centerline valueof the registration structure; and computer-readable program code forconveying the actual centerline value of the registration structure to apatterning apparatus to align a subsequently patterned layer relative tothe registration structure.
 25. A registration system comprising: meansfor obtaining a pair of images of the first material layer of aregistration structure, the registration structure for registering therelative position of a first material layer to the relative position ofa second material layer in a semiconductor wafer, the registrationstructure comprising a centerline value; means for manipulating one ofthe pair of images of the first material layer resulting in a firstflipped image and a non-flipped image of the first material layer; meansfor determining an image centerline value of the first flipped image andthe non-flipped image of the first material layer; means for averagingthe image centerline values of the first flipped image and thenon-flipped image of the first material layer to provide a first offsetcenterline value; means for obtaining a pair of images of the secondmaterial layer of the registration structure; means for determining animage centerline value of each of the images of the second materiallayer; means for averaging the image centerline values of the secondmaterial layer images to provide a second offset centerline value; meansfor comparing the first offset center line value with a second offsetcenterline value to provide a first delta value (Δ₁); means formanipulating a second of the pair of images of the first material layerresulting in first and second flipped images of the first materiallayer; means for determining an image centerline value of the secondflipped image of the first material layer; means for averaging the imagecenterline values of the first and second flipped images to provide athird offset centerline value; means for comparing the third offsetcenter line value to the second offset centerline value to provide asecond delta value (Δ₂); means for subtracting the Δ₁ value from the Δ₂value to provide a Δ_(s) value corresponding to a registrationmeasurement error; means for subtracting the registration measurementerror from the registration structure centerline value to generate acorrected data representative of an actual centerline value of theregistration structure; and means for conveying the actual centerlinevalue of the registration structure to a patterning apparatus to align asubsequently patterned layer relative to the registration structure.